"In order to overcome the issues of poor t­reatment adherence with oral naltrexone, a number of sustained-release implants have been developed internationally for use in alcohol and opioid dependence. A non-randomized retrospective review examined two types of sustained-release naltrexone implants, oral naltrexone, and historical controls revealed a significant difference between immediate and sustained-­release injectable naltrexone in individuals opioid-free 12 months after initiating treatment. Rates combined for the two types of naltrexone implants were 82% opioid free at 12 months compared to 58% opioid free for the oral naltrexone group, and 52% for the historical control group.32"

Source

Kjome, Kimberly L. and Moeller, F. Gerard, "Long-Acting Injectable Naltrexone for the Management of Patients with Opioid Dependence," Substance Abuse: Research and Treatment 2011:5 1–9, doi: 10.4137/SART.S5452.